1. Field of the Invention
The present invention relates generally to hydraulic motors and, more particularly, to a low speed, high torque hydraulic motor.
2. Description of the Related Art
Hydraulic motors are actuators (like hydraulic cylinders) that simply convert hydraulic pressure into rotary movement. Even though the construction is similar, motors differ from pumps in that they are ““pushed”” into rotation by the already active fluid. A hydraulic motor converts hydraulic energy into rotating motion by being pushed by hydraulic fluid. A hydraulic motor is rated by displacement, torque, speed and pressure limits. Further, they are classified as HSLT (High speed/Low torque), LSHT (Low speed/High torque) or Limited Rotation (Torque Actuators). Typical hydraulic motors (actually called a rotary hydraulic actuator) use some form of surface area to receive hydraulic fluid, which cause a shaft to spin, which is connected to various equipment driven by that hydraulic motor. The surface that is ““pushed”” may be rectangular in nature, as in gear, vane and rotary abutment motors, or circular in nature as in rotary and axial piston motors.
Commercially, there are available only several practical designs for low speed, high torque applications. Eaton Corporation Hydraulic Division developed a derivative called the Geroler™, which consists of an inner and outer rotor. The inner rotor has N teeth, and the outer rotor has N+1 teeth. One rotor is located off-center and both rotors rotate. During part of the assembly's rotation cycle, the area between the inner and outer rotor increases, creating a vacuum. This vacuum creates suction, and hence, this part of the cycle is where the intake is located. Then, the area between the rotors decreases, causing compression. During this compression period, fluids can be pumped, or compressed (if they are gaseous fluids). The Eaton Geroler™ design essentially uses bearing rollers instead of lobes on the ring to increase the mechanical efficiency. Greater efficiency comes at the price of greater manufacturing complexity and extreme fit tolerances involving single digit micrometers. Gerotor pumps are generally designed using a trochoidal inner rotor and an outer rotor formed by a circle with intersecting circular arcs. Although this design works well and is simple to define it does create gaps between the inner and outer rotor when the tooth of the inner rotor rotates into the pocket of the outer rotor. This gap seals during rotation causing inefficiency, noise and wear due to the pump attempting to compress the trapped and incompressible fluid in the gap. A Gerotor can also function as a motor. High pressure gas enters the intake area and pushes against the inner and outer rotors, causing both to rotate as the area between the inner and outer rotor increases. During the compression period, the exhaust is pumped out.
However, due to sealing limitations such commercially available hydraulic motors generally maintain a continuous pressure of around 3000 psi, while tolerating only intermittent pressure spikes in excess of that. Nowherein is there available a high torque hydraulic motor that is capable of producing ultra high pressures at speeds ranging from low to high, while still remaining light weight an reliably efficient.
Consequently, a need has therefore been felt for an improved but less complex high pressure, high torque hydraulic motor.